The overall goal of this research program is to investigate the obesity-related changes in microvascular function that initiate the cardiovascular disease process. The growing population of obese adults is predicted to create a large public health burden in the next few decades. Skeletal muscle accounts for the majority of peripheral resistance and glucose uptake in humans. Decreased muscle vasodilation likely contributes to hypertension and sets the stage for hyperglycemia-both hallmarks of metabolic syndrome and diabetes. Thus, low muscle blood flow in obese humans may contribute to reduced exercise capacity-this in turn sets the stage for development of long-term cardiovascular diseases like diabetes. We propose to study younger obese metabolically health adults (18-35 yrs), without confounding effects of age, metabolic syndrome, or diabetes- before the negative effects of obesity can exert their full negative impact. The general hypothesis is that obesity impairs endothelium dependent dilation (EDD) and exercise vasodilation via increased reactive oxygen species (ROS) and reductions in vasodilator signals and increased vasoconstrictor signals. Our preliminary data suggest young obese adults exhibit reduced EDD and exercise vasodilation, and acute ROS scavenging improves both. We will test our hypotheses by arterial drug infusion to test EDD mechanisms in lean and obese humans. We will use similar approaches to test vascular mechanisms controlling blood flow during dynamic exercise. Next, we will test EDD and exercise vascular responses before and after a diet and exercise intervention, where we can parcel out whether physical activity or weight loss plays a larger role in vascular improvements. Finally, we will sample artery endothelial cells from these same subjects to identify molecular pathways that change with obesity as potential therapeutic targets. These studies integrate physiologic, pharmacologic, and molecular approaches to test our hypotheses. We have several exciting preliminary findings that support our hypotheses, and have designed a complementary set of Aims the will soundly address our research questions. A multi-disciplinary, state-of-the-art approach will be used to pursue these aims, which will provide fundamental mechanistic understanding of EDD and exercise mechanisms responsible for reduced blood flow in obese humans. Our novel findings will guide the development of novel therapeutic strategies for obesity and other diseases, including obstructive sleep apnea, metabolic syndrome and diabetes.